1. Technical Field
This invention relates generally to a method and apparatus for cyclically accelerating the leading end of a web material to match the faster speed of a downstream machine component. More specifically, a method and apparatus are disclosed for cutting and subsequently attaching strips of the web material onto a continuous faster moving substrate material.
2. Background Art
Modernly, disposable absorbent articles, such as diapers and catamenial pads, are manufactured utilizing a series of sequential and continuous high-speed operations. In one operation, relatively small fastener strips are cut from a leading end segment of a fastener material and subsequently secured to preselected portions of a continuous web of a substrate material. Traditionally, the substrate material is fed at a relatively high feed rate through a set of applicator rolls while a continuous length of the fastener material is fed at a low feed rate through a series of metering rolls. Moreover, the leading end of the fastener material is typically retained on, or in close proximity to one of the high speed applicator rolls. Thus, once the fastener strip is cut from the leading end of the fastener material, it is retained on the applicator roll for subsequent application to the preselected portion of the substrate material as it passes therethrough.
A problem inherent with such a continuous high speed manufacturing process involves the inability to precisely control the cut length and subsequent placement of the fastener strip due to the large difference in feed rates between the metering rolls and the applicator rolls. In one conventional method, the high velocity applicator roll is allowed to slip beneath the leading end of the fastener material. However, when a knife roll engages and cuts the fastener strip, the leading end of the fastener material is stretched beyond its normal length due to its momentary engagement with the faster underlying applicator roll. Unfortunately, there is a tendency for the remaining leading end of the fastener material to snap back and fall off of the applicator roll following the cutting operation.
Alternatively, it is known to intermittently reduce the velocity of the applicator roll and the knife roll until the fastener strip has been cut. Following the cutting operation, the applicator and knife rolls are rapidly accelerated to their normal rotational velocity. However, such rapid speed changes create undue stress and undesirable cyclical loading on the rolls and their respective drive systems. Moreover, such speed changes commonly result in excessive dimensional variations in the length of the fastener strip as well as inaccurate placement thereof on the substrate material.
Another system for cutting and applying the slow moving fastening material onto the faster moving substrate material uses the high speed applicator and knife rolls in combination with a set of high speed metering rolls. The fastener material is fed onto the applicator roll at high speed and then the metering rolls are rapidly reversed for extracting a predetermined length of the fastener material until the correct segment length is obtained and subsequently cut off. Unfortunately, this system also induces extreme stresses and cyclical loading within the metering rolls and their drive systems while still producing excessive dimensional variations in the final product. Thus, there is a need for an improved method and apparatus for intermittently cutting and applying a slow moving strip of material onto a continuous faster moving substrate material which is not burdened with the above-noted shortcomings.